docs: def hwm93(Z, latitude=0, longitude=0, day=0, seconds=0, f107=150., 
            f107_avg=150., geomagnetic_disturbance_index=4):
      r'''Horizontal Wind Model 1993, for calculating wind velocity in the
      atmosphere as a function of time of year, longitude and latitude, solar 
      activity and earth's geomagnetic disturbance.
      
      The model is described across the publications [1]_, [2]_, and [3]_.
      
      Parameters
      ----------
      Z : float
          Elevation, [m]
      latitude : float, optional
          Latitude, between -90 and 90 [degrees]
      longitude : float, optional
          Longitude, between -180 and 180 or 0 and 360, [degrees]
      day : float, optional
          Day of year, 0-366 [day]
      seconds : float, optional
          Seconds since start of day, in UT1 time; using UTC provides no loss in
          accuracy [s]
      f107 : float, optional
          Daily average 10.7 cm solar flux measurement of the strength of solar  
          emissions on the 100 MHz band centered on 2800 MHz, averaged hourly; in 
          sfu units, which are multiples of 10^-22 W/m^2/Hz; use 150 as a default 
          [W/m^2/Hz]
      f107_avg : float, optional
          81-day sfu average; centered on specified day if possible, otherwise
          use the previous days [W/m^2/Hz]
      geomagnetic_disturbance_index : float, optional
          Average daily `Ap` or also known as planetary magnetic index.
          
      Returns
      -------
      v_north : float
          Wind velocity, meridional (Northward) [m/s]
      v_east : float
          Wind velocity, zonal (Eastward) [m/s]
  
      Examples
      --------
      >>> hwm93(5E5, 45, 50, 365)
      (-73.00312042236328, 0.1485661268234253)
      
      Notes
      -----
      No full description has been published of this model; it has been defined by
      its implementation only. It was written in FORTRAN, and is accessible
      at ftp://hanna.ccmc.gsfc.nasa.gov/pub/modelweb/atmospheric/hwm93/.
      
      F2PY auto-compilation support is not yet currently supported.
      To compile this file, run the following command in a shell after navigating
      to $FLUIDSPATH/fluids/optional/. This should generate the file hwm93.so
      in that directory.
          
      f2py -c hwm93.pyf hwm93.for --f77flags="-std=legacy"
      
      If the module is not compiled, an import error will be raised.
      
      References
      ----------
      .. [1] Hedin, A. E., N. W. Spencer, and T. L. Killeen. "Empirical Global 
         Model of Upper Thermosphere Winds Based on Atmosphere and Dynamics 
         Explorer Satellite Data." Journal of Geophysical Research: Space Physics
         93, no. A9 (September 1, 1988): 9959-78. doi:10.1029/JA093iA09p09959.
      .. [2] Hedin, A. E., M. A. Biondi, R. G. Burnside, G. Hernandez, R. M. 
         Johnson, T. L. Killeen, C. Mazaudier, et al. "Revised Global Model of 
         Thermosphere Winds Using Satellite and Ground-Based Observations." 
         Journal of Geophysical Research: Space Physics 96, no. A5 (May 1, 1991):
         7657-88. doi:10.1029/91JA00251.
      .. [3] Hedin, A. E., E. L. Fleming, A. H. Manson, F. J. Schmidlin, S. K. 
         Avery, R. R. Clark, S. J. Franke, et al. "Empirical Wind Model for the 
         Upper, Middle and Lower Atmosphere." Journal of Atmospheric and 
         Terrestrial Physics 58, no. 13 (September 1996): 1421-47. 
         doi:10.1016/0021-9169(95)00122-0.
      '''
      try:
          from .optional.hwm93 import gws5
      except: # pragma: no cover
          raise ImportError(no_gfortran_error)
      slt_hour = seconds/3600. + longitude/15.
      ans = gws5(day, seconds, Z/1000., latitude, longitude, slt_hour, f107, 
                 f107_avg, geomagnetic_disturbance_index)
      return tuple(ans.tolist())